Hoping some of you guys with high comp engines might be able to answer some questions for me. I am having trouble with detonation and fuel milage. Am getting crappy fuel milage and if I try leaning the fuel or adding more timing I get detonation. I run 91 octane which is the highest octane I can find. Would running an octane booster allow me to add more timing or lean my fuel or maybe both? or would I just be throwing money away? I'm only getting 30 mpg and doesnt seem to change much no matter how I drive. Is this just a trade off for having a engine that makes good numbers? 95" make 100/100 numbers and I am pleased with performance just dont like the milage. Would appreciate any help you guys can give. BTW I think this is an awesome forum with some awesome people. Thanks
Brian

 

Shoot a PM to Dalton or PhilM with details of your build and your ignition. The Mikuni 45 is an awful lot of carb for a 95" engine. The large carb doesn't permit the higher velocity of air to better atomize the fuel droplets that you would have with a smaller carb. Also, iff you are only getting 30 mpg, that's way to rich and may be washing the cylinders of oil. If you pull the dipstick, does it smell like gas?

Hope you get the issue resolved quickly.

 

If 91 octane is all you got, that's all your going to have to work with. 100/100 for a 95 is pretty good. The HC is a good contributor to that. You should be getting better than 30mpg though. I'm somewhere around 45 with my 103 stage 5 at 10.5:1. A good dyno tune should bring your mpg into a better range though. Stay away from the H-D dealer tuner though.

 

Try using "Chevron" high grade fuel for a few tanks. You will find at that compression, your bike will be picky. Plug gap cant be too tight, make sure your gap is open to spec. Octane boost is a retarder for fuel to aid in stalling pre ignition so it might help but try chevron first!

 

30 was all I got on the 95" road queen with a similar build

 

Thanks to everyone for the responses. Went out and pulled the dipstick to see if the oil smelled of gas and no gas smell. Pulled the plugs to have another look at them and they werent perfect but do not think it is overly rich. Had leaned it out a little but went back to richer setting because it started pinging. I attached a half a$$ picture of the plugs..

 

I'm running a similar build on my 99 FLHT w/Mikuni 42 and 37g cams. Screamin' Eagle heads and when I stop for gas I sometimes get an engine lock on start up so I know I should be running compression releases. I thinking it's 10:1 compression or close to it.

I get around 35-39 mpg depending on where I'm riding.

 

Retard the ignition timing 2-3 degrees.

 

Adjust timing and try a colder plug. I would go two heat ranges colder and see how it works for you.

 

I built a 95" that made 111hp/113tq and used the Mikuni 45, Woods TW9 650 lift cams. I went 1 size smaller on the main jet. Timing and fuel should be adjusted on a Dyno for air to fuel ratio, AFR. I will admit it was very fussy about jetting, two sizes smaller and power really dropped, one larger and it looked like a diesel on a dyno. My Wide Glide didn't spark knock at all. I used a Daytona Twin Tech Ignition with settings per the manufacture instruction sheet, standard heat range plugs and premium fuel. CCW that Dynoed the bike was amazed how it ran, not just on the dyno but on the street. Fuel mileage was about mid / upper 30's. Octane additives work just a PITA.